Addition and subtraction : Khan Academy on a Stick

Khan Academy on a Stick

Arithmetic

Basic addition
Introduction to addition. Multiple visual ways to represent addition.
Basic subtraction
Introduction to subtraction

Intro to addition and subtraction

Adding and subtracting is the basis of all mathematics. This tutorial introduces you to one-digit addition and subtraction. You might become pretty familiar with the number line too!

Example: Adding two digit numbers (no carrying)
Adding Whole Numbers and Applications 1
Subtraction 2
Different ways to view subtraction
Example: 2-digit subtraction (no borrowing)
Subtracting Whole Numbers
Level 2 addition
Adding a 2 digit number to a 1 digit number. Introduction to carrying.

Two digit addition and subtraction

In this tutorial, we'll start adding and subtracting numbers that have two (yes, two!) digits. We won't be doing any carrying or borrowing (you'll learn what those are shortly) so you can see that adding or subtracting two digit numbers is really just an extension of what you already know.

Adding: three digit numbers
We're going to learn all about carrying when adding a 3 digit number. Join us!
Adding: why carrying works
Sometimes when we add, we carry our tens to the next column. Let's watch this so we can understand why it works.
Adding: three digit numbers and regrouping
In the old days 'regrouping' was known as "carrying." It's the same idea now as then: moving the tens (or hundreds or thousands) over to the next column.
Addition 4
More practice carrying with multiple digit numbers

Addition with carrying

You're somewhat familar with adding, say, 17+12 or 21+32, but what happens for 13+19? Essentially, what happens when I max out the "ones place". In this tutorial, we'll introduce you to the powerful tool of carrying and why it works.

Subtracting: three digit numbers and basic regrouping
Subtracting multi-digit numbers can be a little confusing when the top digits are smaller than the bottom ones. Let's look at regrouping together. It will help!
Subtracting: three digit numbers and regrouping
When we don't have enough of something, we sometimes borrow it. Same in math! When there aren't enough tens (or hundreds, etc) to subtract with, we can borrow (also called regrouping).
Subtracting: regrouping twice
Getting a little fancier with our regrouping now. What if you have TWO numbers that require you to borrow or regroup? You guessed it! You have to take value from one place and give it to another.
Subtracting: Regrouping from zero
In Kindergarten you learned the importance of sharing, right? In math, when we lack value in a number to subtract with you borrow or regroup from a neighbor. Sometimes you borrow from the tens...but what if you have zero tens? Ha....let's watch this and learn!
Borrowing once example 1
Borrowing once example 2
Regrouping (borrowing) twice example
Alternate mental subtraction method
How I subtract in my head

Subtraction with borrowing (regrouping)

You can subtract 21 from 45, but are a bit perplexed trying to subtract 26 from 45 (how do you subtract the 6 in 26 from the 5 in 45). This tutorial is your answer. You'll see that we can essentially "regroup" the value in a number from one place to another to solve your problem. This is also often called borrowing (although it is like "borrowing" sugar from your neighbor in that you never give it back).